Combine the cake mix, oil, egg whites, and water in a mixing bowl. Beat with an electric mixer on low speed for 30 seconds, then increase the speed to medium and beat for 2 minutes, scraping down the sides of the bowl. Stir in the chopped bittersweet chocolate and scoop the batter into the cupcake liners, filling them two-thirds full.

Bake in the preheated oven until golden and the tops spring back when lightly pressed, 15 to 20 minutes. A toothpick inserted into the center of a cupcake should come out clean. Remove the cupcakes from the pans and cool completely on wire racks.

Remove the centers of the cupcakes using an apple corer or paring knife, cutting out the middles in a funnel shape by holding the knife at a 45-degree angle. Spoon or pipe the filling into the cupcakes. Refrigerate the cupcakes while you prepare the ganache.

Place the semisweet chocolate pieces in a heat-safe bowl. Bring 1/2 cup heavy cream to a boil. Pour the hot cream over the chocolate; cover the bowl and set aside for 5 minutes. Whisk the chocolate and cream until well combined; allow the ganache to cool until it reaches a spreadable consistency, about 1 hour. Spread a spoonful of ganache evenly over each cupcake. Refrigerate the cupcakes while you prepare the frosting.

Melt the white chocolate chips in a microwave-safe bowl by heating for 1 minute, stirring after 30 seconds. Allow the white chocolate to cool until almost room temperature but still fluid. Cream the butter and cream cheese together. Blend in the melted white chocolate, vanilla extract, and food coloring (if using). Spread the frosting on the cupcakes. Serve immediately, or refrigerate until serving.